Facebook is dramatically expanding its engineering center in Seattle, leasing a huge chunk of office space in the South Lake Union neighborhood that is also home to Amazon and a future campus for Google.

Facebook is taking the 333 Dexter project, which totals 630,000 square feet in a pair of 12-story buildings and a 15-story tower called Dexter Yard that has 500,000 square feet of space and was originally designed for biotech companies, according to a report from the Puget Sound Business Journal. Real estate sources who were not directly involved, but have knowledge of the situation, confirmed 333 Dexter to GeekWire, though one source said a lease has not been signed. They could not verify the lease at Dexter Yard.

Together, the two projects total more than 1.13 million square feet of office space.

The new leases mark the continuation of Facebook’s love affair with Seattle — which is quickly becoming a major engineering center for the social media giant. Facebook also is rapidly expanding its Oculus virtual reality team in the Seattle area, mining the region’s rich history of gaming and software talent. The Mark Zuckerberg-led company first set up shop in Seattle in 2010, part of a wave of Silicon Valley tech giants that have set up beachheads in Seattle.

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And while Facebook is excited about Seattle’s burgeoning South Lake Union neighborhood, that’s not the only place it’s expanding.

In Microsoft’s hometown of Redmond, Wash., where Facebook is building out a massive campus for Oculus/Facebook Reality Labs, the company is reportedly teeing up a 650,000-square-foot office project under the mysterious moniker of “Building X” on a site it bought earlier this year. The project would push the growing Redmond campus well over one million square feet.

The 333 Dexter project is under construction and expected to open next summer, according to the project’s website. The site was the location of KING Broadcasting’s long-time headquarters building, which was razed to make way for the project. Dexter Yard is slated to be completed in 2021.

Facebook representatives declined to comment, and representatives of BioMed Realty, the developer of Dexter Yard, and Kilroy Realty Corp., which is building 333 Dexter, did not immediately return requests for comment.

Amazon’s original 11-building campus in South Lake Union, first announced in 2007, totaled 1.7 million square feet but has since expanded far beyond that. Google is taking a three-block campus in the neighborhood that totals about 930,000 square feet.

Facebook added more than 10,000 people worldwide in the past year, a 45 percent increase that brings its total headcount to 33,606 people as of Sept. 30, according to numbers disclosed in its third-quarter results. Facebook added more than 3,300 people in the last three months alone.

Nat Levy is a staff reporter at Geekwire covering a variety of technology topics, including Microsoft, Amazon, tech startups, and the intersection of technology with real estate, courts and government. Contact him at nat@geekwire.com and follow him on Twitter at @natjlevy.

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